Studies are planned to determine which cells in lymphatic tissue are insulin sensitive, and to what extent the integrity of lymphatic tissue is insulin dependent. Thymocytes will be fractionated on nylon-wool columns, by density gradient centrifugation, and affinity chromatography on Sepharose-insulin columns. Subpopulations of thymocytes will be characterized for insulin binding, the effect of insulin on glucose metabolism, and activity of terminal deoxynucleotidyl transferase. The effect of insulin will be further characterized by determining the conditions for an optimal insulin response. Parameters that will be examined are ionic milieu, pH, temperature, buffer, etc. Insulin binding to, and the effect of insulin on, glucose metabolism of thymocytes from diabetic rats will be examined. Thymus tissue will be involuted with glucocorticoid administration and its growth and regeneration monitored in normal and diabetic rats by measuring the incorporation of 3H-deoxynucleotides into thymic DNA. These studies will lead to a better understanding of the interaction of insulin with lymphatic tissue, and will shed light on the immunological defects observed in the diabetic individual.